diff --git a/tape/tag.go b/tape/tag.go
index a2a9fd4..4e9db37 100644
--- a/tape/tag.go
+++ b/tape/tag.go
@@ -25,6 +25,10 @@ func (tag Tag) WithCN(cn int) Tag {
 	return (tag & TNMask) | Tag(cn % 32)
 }
 
+func (tag Tag) WithoutCN() Tag {
+	return tag.WithCN(0)
+}
+
 func (tag Tag) Is(other Tag) bool {
 	return tag.TN() == other.TN()
 }